1. Field of the Invention
The present invention relates generally to a belt or chain tensioning device and particularly concerns such a device which automatically releases a preset biasing force during installation.
2. Description of Prior Developments
Belt tensioning devices are well known and exist in numerous forms. A common arrangement includes a tensioning member, commonly a torsion spring, which urges a belt-tensioning idler pulley against an endless belt to control the tension in the belt and to maintain the engagement of the belt with its associated pulleys. It is necessary to control belt tension in order to prevent the belt from slipping about the pulleys over which the belt travels and for controlling belt wear, and often to maintain the angular relationship among the pulleys of synchronous drive systems.
Some tensioning devices are provided to manufacturers in a biased or spring-loaded state for facilitating installation and assembly within chain or belt driven systems. Such devices may include a prewound torsion spring which is held in a biased state between a mandrel and a pulley hub.
A spring release mechanism provided for allowing an installer to manually release the preset spring force between the mandrel and hub after the tensioning device has been installed within a belt driven system such as a timing belt assembly or automotive accessory drive system. Actuation of the release mechanism permits the hub to drive a tensioning pulley against an endless belt or the like. Examples of such release mechanisms are shown in U.S. Pat. No. 4,808,148 which discloses a ratchet and pawl release mechanism and U.S. Pat. No. 4,832,665 which discloses a grenade pin type release mechanism.
Although such prior release mechanisms perform adequately for their intended purposes, there have been instances where an installer has inadvertently omitted releasing the spring tension by forgetting to actuate the release mechanism. In these cases, the belt tension is not adequately controlled or maintained. This can lead to premature belt failure or poor belt performance. In some cases, this can lead to further damage such as valve failure in the case of a belt-driven timing mechanism. Moreover, grenade pin release mechanisms create a waste problem once the pins have been removed. Although the pins can be recycled, this has not proven an attractive solution.
Accordingly, a need exists for a tensioning device which virtually ensures the release of a preset biasing force by automatically releasing this force during the installation of the tensioning device within an associated belt or chain-driven system.